1. Field of the Invention
The present invention relates to a rear suspension controller for a vehicle, particularly to a rear suspension controller which is effective against a shock caused by a sporadic bump or dip of a road surface on which the vehicle is running.
2. Prior Art
Conventionally, spring constant, damping force, bush characteristic or stabilizer characteristic of various suspension units provided between a vehicle body and its wheels is altered depending on conditions of the road surface or running conditions of the vehicle, not only to prevent the vehicle from having shocks or vibration for improving ride comfort but also to keep controllability and stability of the vehicle.
For example, there are inventions to alter the spring constant of air spring for an air suspension in response to the state of the road surface such as Published Unexamined Patent Application No. Sho 59-26638, those to alter the damping force of a shock absorber as well as the spring constant of an air spring such as Published Unexamined Patent Application No. Sho 59-23712, those to alter the damping force of a shock absorber only such as Published Unexamined Patent Application No. Sho 58-30542, those to alter just the ridigity of a bush such as Published Unexamined Utility Model Application No. Sho 59-132408 and those to alter the rigidity of a stabilizer such as Published Unexamined Utility Model Application Nos. Sho 59-129613 and 59-135213.
The above-mentioned controllers detect the bad driving condition of the road surface by a vehicle height sensor, alter a characteristic of each suspension, maintain the controllability and stability on the bad driving condition and prevent dive, squat, rolling, etc. in case of predicting the sudden change of vehicle posture e.g., dive, squat, rolling, etc. by brake lamp switch, throttle position sensor and steering sensor.
However, such prior controllers judge the bad driving condition only after the severe changes are detected continuously by the vehicle height sensor or the vehicle height alteration acceleration sensor in a predetermined period and alter the suspension characteristics for all the wheels so as to achieve a predetermined effect. In such cases, they do not alter the suspension characteristics when passing over other kinds of shock like a joint of road patches, a sporadic bump or dip of a road surface, because they resume running on a flat road after receiving a sporadic shock.
Accordingly, there are problems such as an the impossibility of preventing uncomfortable shock for passengers during running on a road surface with the above-mentioned sporadic bump or dip different from rough road running, and controllability, stability, characteristics of vibration and noise are deteriorated after passing over the bump or dip.